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Old 30th September 2011, 02:16 PM   #1
udailey is offline udailey  United States
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Default A/B testing board for high power amps

A buddy of mine manufactures ClassD amps. He wants to compare 3 different modules and asked if I would build a board that will A/B/C them.
The idea is obvious: 12 relays with 4 per circuit of which 2 go to each module/speaker.
I dont want to have huge pops when the relays clap together as we will probably be listening at high volume and there will be significant voltage/current potential.
Should I solve the problem with a cap from + to - of the amp output/speaker input? This would be a bit like when we put a cap across the on/off switch to remove popping. Well, visualizing it now.. with cap on on/off switch its not from + to - its just from one side of the contact to the other, so perhaps I should approach it that way.
Question is.. What value cap should I use? What rating would you suggest as these amps have kilowatt capabilities?
Thanks guys/gals
Uriah
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Old 1st October 2011, 08:22 PM   #2
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Try 100nf
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Old 1st October 2011, 08:29 PM   #3
udailey is offline udailey  United States
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.1uf is much to high. Dont mean to be daft as I do appreciate the answer. I dont know the right value, but .1uf will allow music to pass through. High frequency music but it will be audible. I need a picofarad value most likely but I dont know what value.
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Old 1st October 2011, 08:47 PM   #4
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You may want to think about using the relays to mute the inputs and put an 8 ohm load on the outputs of the amplifiers which are not feeding the speakers.
When selected, the amplifier input would un-mute and the output would be disconnected from the load resistor and connected to the speaker.
With no audio going through the amplifier, the output load resistors could be quite small.
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Old 1st October 2011, 08:50 PM   #5
udailey is offline udailey  United States
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Thanks Frank. We want the same signal going to each amp full time so we can instantly switch between amps so that my audio memory isnt lost as it only takes a few seconds for me to lose the feeling of the quality of the music coming from one amp when switching to the next.
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Old 1st October 2011, 08:54 PM   #6
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The same relay which switches the output can also mute and un-mute the input.
No delay at all.
The only other option would be to put a BIG load resistor on the output of each channel of the amplifiers which are not selected to feed the speaker.
I don't think that a capacitor on the output will provide the proper loading. Worse case would be a tuned circuit at certain frequencies.
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Old 1st October 2011, 08:59 PM   #7
udailey is offline udailey  United States
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A cap is only to reduce the pop I expect when the relay closes. Like flicking the ON/OFF switch on your amp. Without a cap across its contacts it will arc and you will hear that arc as a pop in your speakers.
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